The broad, long-term aim of this study is to understand the neural mechanisms of tactile spatial perception in the human hand. Impaired tactile acuity leads to the inability to perform simple tasks such as buttoning and unbuttoning a button. Tactile spatial acuity is impaired in advanced age and in many neurological conditions. Understanding the underlying mechanisms is an essential first step in any treatment. The long-term aim of the study proposed here is to understand the neural mechanisms of tactile spatial perception in primary somatosensory (SI) cortex. A basic problem is that the functional organization of SI cortex is not well understood and this makes it difficult to formulate and test specific hypotheses. Combined psychophysical and neurophysiological studies over the last forty years have lead us to understand that the human hand is innervated by four types of mechanoreceptors and that each is responsible for a distinctly different aspect of tactile perception. Despite the distinct functional division evident in the peripheral nerve and despite the widespread, and justified belief that the information conveyed by the four afferent groups remains segregated within the central nervous system, the division of function within SI cortex is understood only in very broad terms. One reason is the lack of flexible, controlled stimuli with which to study the functions of neurons in St cortex, which we believe we have overcome with the development of a tactile stimulator with 400 independently controlled probes. Experiments proposed in Aim 1 examine the response properties of neurons in areas 3a, 3b, 1, and 2 of macaque SI cortex with temporal and spatial stimuli selected to span a wide range of tactile function. Experiments proposed in Aim 2 examine differences in the mechanisms underlying neuronal response properties in these areas using random stimuli and regression analyses. Experiments proposed in Aim 3 examine the neural mechanisms of tactile spatial perception with stimuli that have been particularly effective in previous studies (square-wave gratings) and with a new class of stimuli that combine the spatial and temporal properties of tactile function in a single framework (spatiotemporal sinusoids). [unreadable] [unreadable]